Myeloid Sarcoma in Patients with RUNX1/RUNX1T1 Positive AML and a c-kit Mutation

t (8;21)(q22;q22) is the most frequently detected cytogenetic abnormality in patients with acute myeloid leukemia (AML) and accounts for 8-21 % of de novo AML. The translocation involves two genes, RUNX1 (formerly AML1) on 21q22 and RUNX1T1 (ETO) on 8q22. RUNX1/RUNX1T1 translocation confers a favorable prognosis, but a subset of patients has a precipitous course with a high incidence of relapse. This patient subset is associated with the presence of a c-kit mutation. c-kit is a proto-oncogene, which encodes a type III transmembrane tyrosine kinase, which elicits a variety of cellular responses essential for the development of bone marrow stem cells. The expression of the c-kit mutation in AML is < 2%, whereas AML with RUNX1/RUNX1T1 shows higher rates of c-kit mutation and is associated with extramedullary leukemia and poor clinical outcome. We report cases of myeloid sarcoma in patients with RUNX1/RUNX1T1-positive AML and a c-kit mutation. (Korean J Med 2011;81:517-525